popping through intake.... sorry...

I thought popping or back fire through the intake was rich condition but Im not sure.

stangster50 said:

i searched, but didnt find something too similar to mine.... ok....

b-cam, gt40x heads..

the car i got to sorta idle on its own by messing with fuel pressure.... it pops really bad through intake, and dosent really want to stay running.... changing fuel pressure seems to help.... a noticeable difference when covering mass air a little... (90) i really dont want to keep starting it like this... timing sorta helps.... it either dosent want to run, and sounds weak, or will run, and starts up at full throttle it sounds like.... im wondering about maybe adjusting the valves wrong.... but i really dont know... im pretty discouraged, because i want to make stang week...

thanks guys.

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What do you have the timing and fuel pressure set at? Popping is usually either timing or if lean they'll pop when you try to accelerate.

stangster50 said:

tried pressure anyhere from 40-60.. tried timing all positions.... pops while idling... barely runs... kinda clears up with giving it more throttle...

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When you say you tried the timing at all positions does that mean you didn't time it with a light? You may be a tooth off on the distributor. Timing for you should be around 14 degrees with the spout removed.

Redline_351R said:

I thought popping or back fire through the intake was rich condition but Im not sure.

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Definitely sounds like unburnt fuel igniting.

I've never had a popping from a rich mixture. Symptoms for that are sluggish, black smoke from exhaust. Pull a plug see what they look like. Sounds like timing to me. Also double check your firing order.

Yes

Yes, popping through intake is usually either a lean condition or a timing problem.

justagt said:

Yes, popping through intake is usually either a lean condition or a timing problem.

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Perhaps I was thinking rich as popping through the exhaust?

Popping through the intake is usually caused by not having the valves adjusted properly. What is happening is the intake valve is not all the way closed when the piston is coming up the cylinder and instead of compressing the air, it is popping it back out the intake valve and up through the intake mainfold. Air should be drawn into the cylinder, then the intake valve should close all the way and then the piston can come up and compress the air/fuel. It sounds like you have them adjusted too tightly, or the cam is an indexed cam and it is indexed to the advanced side. First thing I'd check is the valve adjustment. Rotate the engine until cylinder #1 is at TDC on the compression stroke... get zero lash on both valves and then turn the nut a little more than HALF a turn more. Rotate the crank 1/4 turn and do the cylinder that is next on the firing order... then turn the crank 1/4 turn more and do the next cylinder on the firing order. You will have to rotate the crank two full revolutions to do all eight cylinders... and you will be back to cylinder #1 at TDC on the compression stroke. If you still have the popping, then you must find out if you have an indexed cam and how it was installed. If it's not the cam, then you may have some bad valve seats that are leaking. The valves must seal 100% to NOT have popping. You can check if the valves are sealing by doing a compression test. I hope this has helped.

Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches.

Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF on Mass Air cars (89-95 models).
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
E.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
F.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow.
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/





If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

stangster50 said:

ok.... so i measured compression... highest was 170, lowest was 160.... so i messed with timing again.... as i had the car running every time it popped i notices a lil poof of smoke coming from in between the head/intake..... so i pulled the intake off and every port was leaking..... i guess i had gotten stock intake gaskets when i needed bigger ported ones for the gt40X heads? i thought the stock ones were good to an extent......

so... i guess im an idiot? which intake gaskets should i use?

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Jeez don't be so hard on yourself. It takes time to get the bugs out of this stuff. You want a Felpro 1250 probably for the GT40 X heads. Go for the 1250-S, they have a steel core and hold up alot better. At least you found the source of the popping. Massive vacuum leak / lean condition. Good luck with it.

Glad you got it... I had the same problem when I installed my typhoon on my gt-40x's. Add a thin layer of silicone to all the mating surfaces (both sides of the gasket) for a better seal.

I brought it to a shop because I couldn't figure it out for so long... I was so happy when I finished, I drove around without a hood all day...(who needs one?)

Get the good gaskets now, stockers will work with silicone, but you'll end up blocking the ports here and there...